February 20, 2020
Doug Dietrich, AIA, CSI, CDT
Although the means and methods are the responsibility of the general contractor and subcontracted trades, it is wise to conduct a deeper dive into the installation ‘nuts and bolts’ to better understand possible areas for creative collaboration resulting in a cohesive building envelope.
Curtain wall installation requirements, means, methods, and materials continue to evolve, yet many of the basics remain the same. Most curtain walls have similar installations, but differ on size, location, alignment, and anchorage of components. Here are some of the critical areas to focus on for a successful curtain wall installation.
1. Failure to correctly size or properly position weep holes in the curtain wall pressure plates and covers are all too common. The drainage path and the size, type, location, and frequency of weep holes vary by manufacturer. Some systems are weeped via holes in the bottom of the covers and others at the ends through the joint between the horizontal at vertical cover intersection. For example, if the weep is located too high, it will trap water in the glazing pocket causing the bottom of the insulated glass unit (IGU) to sit in water, and likely, voiding warranty. Weeping strategy must be clearly identified in installation instructions and shop drawings according to the manufacturers’ requirements.
2. Failure to prepare additional pressure plate fastener holes can occur when an installing contractor needs to modify material in the field. Additional fastener holes should be prepared at the ends of the pressure plate to provide adequate pressure. The types of pressure plates and their required compression can be unique to each manufacturer, but fastener holes typically are within 50 mm (2 in.) of the vertical member. In simple terms, it is advisable to ensure the correct screws are put in at the proper place with the appropriate torque.
3. Failure to seal around the front of shear blocks, and along the front edges of horizontal sections can lead to air and water infiltration. When it comes to sealant, more is not better. Too much sealant can plug weeps and mask leaks making troubleshooting very difficult.
4. Failure to install or properly seal the water dams or zone dams can lead to serious damage. Water dams are a critical component in typical curtain wall systems. They are installed at the horizontal to vertical frame intersections to keep the water compartmentalized at each lite. The water dams at structural glazed verticals also should be sealed on their horizontal tongues. Additionally, sealant should be applied to the water dam’s frame prior to installing the vertical pressure plate. If a water or zone dam is accidentally left out or improperly sealed, water will drain down to next lite and can flood the system.
5. Failure to seal other key connections can result in the curtain wall system’s poor performance and water damage to critical areas. Sealant must be applied to the horizontal gasket abutting the vertical gasket. It also needs to be between the horizontal pressure plate and the vertical cover. Finally, it is recommended to ensure sealant is applied around the base of the vertical mullion running to the building substrate at an entrance.
To avoid these common failures, it is best to review each curtain wall manufacturer’s guidelines. Additional best practices include specifying performance mockups are tested prior to installation and field testing occurs early in the built phase. Some specifications will also indicate the work must be done by experienced and certified installing contractors. Helping prevent these key points of failure will further ensure the curtain wall meets the required performance.
The opinions expressed in Failures are based on the authors’ experiences and do not necessarily reflect those of The Construction Specifier or CSI.
Doug Dietrich, AIA, CSI, CDT, is an architectural representative with Tubelite Inc. He is an architect with more than 30 years of experience helping building teams achieve energy efficiency, structural compliance, condensation resistance, and blast hazard and hurricane mitigation. Doug can be reached at email@example.com.
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